In recent optical communication, introduction of wavelength division multiplexing (WDM) has enhanced a high capacity network, and in order to achieve much higher capacity, further cost reduction, and lower power consumption, a technique transmitting an optical signal without performing optical/electrical/optical conversion has been developed.
In particular, an optical path network in which routing is performed by optical circuit switching, instead of packet switching (Kiyo Ishii, Jyunya Kurumida and Shu Namiki, “Toward large-capacity, energy-efficient, and sustainable communication networks”, Synthesiology, vol. 7, no. 1, AIST, pp. 43-56.) achieves low delay and low power consumption by several orders of magnitude, and introduction of the optical path network to a data center has been also considered.
In such optical path network, a network management system collectively manages a plurality of optical nodes arranged, and an optical path whose bandwidth is compensated is provided between arbitrary end users.
The optical node is linked to an adjacent optical node through an optical fiber and has a function of outputting an arbitrary wavelength signal received by an arbitrary input port to an arbitrary output port.
The optical node may have various possible configurations, and in any cases, the optical node can be expressed as a switch having a plurality of input/output ports as in FIG. 1.
To an input port, a transmission signal from an adjacent optical node and an added client signal are input.
From an output port, a transmission signal to an adjacent optical node and a dropped client signal are output.
When the optical node has a small number of ports, the optical node can be configured such that an optical switch and a wavelength selective switch (WSS) can be used in combination.
FIG. 2 illustrates a configuration example in which an arrayed waveguide grating (AWG) and an optical switch are used in combination.
In this case, a WSS on an output side may be substituted by an optical multiplexer.
FIG. 3 illustrates a configuration example in which a (1 input, N output) WSS is used.
In this case, although a (1×N) WSS is used on both sides of input and output, one of them may be substituted by an optical splitter (splitter), and the number of ports N may not be in common to all WSSs.
For example, as a modification of FIG. 3, an asymmetric configuration illustrated in FIG. 4 may also be adopted.
In the configuration in FIG. 4, the optical splitter and the WSS inside are omitted in input/output ports #4 to #6. However, connecting an AWG, a transponder aggregator (TPA), and the like to these input/output ports can provide variation in the configuration of the optical node.
The TPA is also called a multicast switch and used in multiplexing/demultiplexing wavelengths of a plurality of client signals.
A typical TPA is a combination of an optical splitter and an optical switch, and its configuration example will be illustrated in FIG. 5.
Small-scale optical nodes illustrated in FIG. 2 to FIG. 4 are referred to as a wavelength cross connect (WXC) herein.
A large-scale optical node having several tens to several hundreds of ports is achieved by making a switch with a different switching granularity in a multilayer structure (Kiyo Ishii, Jyunya Kurumida and Shu Namiki, “Toward large-capacity, energy-efficient, and sustainable communication networks”, Synthesiology, vol. 7, no. 1, AIST, pp. 43-56.).
FIG. 6 illustrates an optical node in a three-layer structure in which an OXC (optical cross connect) serving as an optical switch (FXC: fiber cross connect) switching a signal in units of a fiber, the above-described WXC switching a signal in units of a wavelength, and an optical data unit (ODU) switch switching an electrical path in units of time are arranged in three levels in combination.
Meanwhile, in order to understand an operation condition of an optical path network and detect a trouble, it is necessary to know signal flow on the network.
As a method therefor, Goji Nakagawa and others, “Demonstration of Real-time FSK Light Labaling using DAC-Based Transmitter for 400G Superchannel”, 41th European Conference of Optical Communication (ECOC2015) Proceedings, Tu. 3. 5. 6, Valencia, Spain (2015), indicates a method in which identification information related to a transmitter is assigned to an optical signal upon transmission.
In this method, an optical node needs to recognize the identification information which is assigned to the signal. Accordingly, this optical node has a property dedicated to the transmitter used on the network.
When scalability and flexible operation of a network are considered, it is desirable that the optical node does not depend on a type of a transmitter and a transmission scheme to be used on the network, in other words, the optical node can be used for an arbitrary signal.
To achieve such purposes, it is necessary that the optical node has a function of monitoring signal flow inside the node by itself.
FIG. 7 illustrates a display example of a path monitoring in the optical node. For simplicity, an optical signal is compliant with the DWDM (dense wavelength division multiplexing) grid, and a center wavelength in the n-th grid is displayed as λn.
Also, due to a space on the paper, signals corresponding to eight DWDM grids (λ1 to λ8) only are displayed.
This path monitoring displays a wavelength of an optical signal output from each output port of an optical node and a port number to which the output optical signal is input.
When the optical node has such monitoring function, it is possible to constantly monitor signal flow on the network and build an optical path network having higher scalability.